Magnetic clamp



W. C. BARNES ET AL MAGNETIC CLAMP June 11, 1940.

Filed March 12, 1937 Patented June 1 1 1940 mom-mo Walter G. Barnes, Lake 31nd, and Henry W. i

The present invention relates to a magnetic- 1 clamp for quickly establishing a pressure contact 1 between an electrical conductor and ametallic body. It is primarily intendedifor use in connection with flaw detector apparatus of the type which is now commonly used by American railroads for locating hidden fissures in rails, but its use is not necessarily limited to this field.

The advantages of the clamp will become ap--' parent as the disclosure proceeds and the description is read .in conjunction with the accompanying drawing inwhich Fig. 1 is a diagrammatic view of a rail test car showing the compressed air; contact sus-- pended from the car and the magnetic rail clamp for completing the electrical circuit over one of the rails; r

Fig. 2 is an enlarged'plan view of the :rail clamp shown in Fig. 1;'

shown in Fig. 2; Fig. 4isa transverse'sectional' view taken on the.line 44 of Fig. 3 and showing the relative positions of the various parts of the clamp before 85 the metallicfyoke is forced into contact with the rail; and

Fig. 5 is a sectional view corresponding to Fig. 4 but showing the relation-of the elements when the yoke is magnetically gripping the rail.

In the illustrative embodiment of the inven tion in which the magnetic clamp is shown associated with the detector car for locating flaws in' the track, the clamp constitutes a part of the hand check apparatus which is used to more 35 accurately locate and analyze a flaw which previously had been approximatelylocated by means of the flaw detection apparatus carried by the car; and since this latter apparatus constitutes no part' of the present invention, there is no necessity to describe it here.

The hand check apparatus commonly used operates on the principle that when a current of constant strength is passed through a rail the difference of potential between two points a knowndistance apart moved along the rail will 46 be a constant value so. long as the rail isa homogeneous body, but should these points traverse a portion of the rail which is non-homoge'neous there will'be a change in thispotential 50 difference.

sists of a pair of contact points spaced a known distance apart and adapted to engage the top' Fig. 3 is a side elevational view of the clamp Apparatus used for this purpose usually conpassed through the rail in some suitable man- Keevil, Highland Park, Ill. Application March 12, 1937, Serial No. 130,586

e (curs-213 nr and as the contact points are moved over the energized portion. of the rail the potential diilerence between the contact points is reg- -equipment generally indicated at {22.

istered on a voltmeter placed in the. circuit with the contactpoints. The voltmeter reading will 5 remain substantially constant untila flaw ordiscontinuity is traversed, and then there will j be a comparatively sharp deflection of the voltmeter needle. v

For the purpose of passing electrical current 10 through the rail, it is convenient to have one contact mounted on the test car and operated by compressed air and the other contact manually. applied to 'the.rail.- 'I'hislattercontact is the subject matter of the present invention.

A preferred form of the invention has been shown in the drawing and will be described for the purpose of complying with section 4888 oi.

the Revised Statutes, but it will be understood that the appended claims are not limited to the specific disclosure but should be construed as broadly as the prior art will permit. Referring now to the drawing, Fig; 1 shows a rail test car generally indicated at H adapted to travel along rails I2 and I3 and provided with 2 suitable rail contact members I! and ,l! each of which is secured to the end of a shaft constituting a part of the hand check cylinder The cylinders are mounted on the car' body in any suitable' manner, and are 'operatively connected to a source of compressed air in response to controls operated, preferably, from within the car.

A clamp it constitutes the other electrical contact for completing the circuit. Electrical current may be furnished by means ,0! a generator l-l mounted in the car and connected in "series with the rail contacts through conductors The magnetic clamp "is best shown in Figs. 40 2-5, inclusive; and comprises a terminal block 25, preferably of brass or copper,' and having a rail-engaging headltprojecting downwardly beyond the mainjbody of the blocl nf A-heel 28 of a suitable insulating material such. as Bakelite is secured-to the opposite end oitheblock, by means of a countersunk machine screw-'28 in. order to limitthe passage of current from ,the block to the rail through the head It. Thus it is seen that all of the current passing into the U rail must necessarily enter at the forward end,

of the terminal block 25 andthen pass backwardly through the/fail to the contact II. The reason' for this arrangement is to/insu're a latively strong magnetic'fleldaround-the terminal block in the vicinity of a magnetizable yoke 35 which straddles the terminal block, as best shown in Figs. 3-5, inclusiveu I The yoke 35 may be made of mild steel or other suitable magnetizable material and is supported on the terminal block by means of a leaf spring 36 secured to the terminal block by machine screws 31 and 38 and to the yoke or armature 35 by screws 39 and 40. Insulating material 41 such as Bakelite is inserted between the spring and the yoke in order to prevent current from passing through the spring 36 and yoke 35 to the rail when the yoke is in engagement with the rail.

In its normal position the yoke 35 is held slightly away from the rail by the spring 36 as shown at-42, and in actual practice a distance of approximately of an inch has been found to be satisfactory. -A similar distance should be maintained between the legs 43 and 44 of the yoke and the block 25 so that the current in the block cannot pass into the rail through the legs of the yoke.

The spring 36 must be sufllciently strong to hold the yoke normally out of engagement with the rail, although it must permit engagement when reasonable manual force is applied at the top of the yoke. 4

When it is desired to make a hand check of a certain portion of the rail l2, the test car is stopped and the contact l4 lowered against the rail. The hand clamp I6 is then removed from the side of the car, where itis suspended when not in use, on a suitable hook (not shown) which passes through an opening in a boss 3| at the head of the terminal block, and is placed on the rail as shown in Fig. l. The generator I! is then placed into operation causing a current to flow through theconductor 18, secured to an extension 32 of the terminal block 25, and thence into the rail at 26 as shown in Fig. 3. This current passing through the terminal block 25 creates a magnetic field around the block, and since lines of magnetic flux take the path of least resistance, this field is concentrated in the yoke 35. In the normal position of the yoke, however, due to the gap in the magnetic circuit, a relatively high reluctance is present in the magnetic circuit. When the yoke is manually urged into contact with the rail as shown. in Fig. 5, this air gap is closed thereby greatly reducing the reluctance in the circuit and causing the yoke to firmly grip the rail. This lowering of the yoke causes the spring 36 to press down on the two ends of the terminal block 25, and as long as the yoke is in engagement with the rail, the terminal block is held securely against the rail by the spring. The magnetic clamp may easily be removed from the track by merely shutting off the generator, whereupon the magnetic field in the yoke 35 collapses and the spring 36 lifts the yoke from the rails We claim: v

1. A magnetic clamp adapted to establish a pressure contact between an electrical conductor and a magnetizable body; said clamp com.-

prising a terminal block, an armature normally held out of contact with the block when said block is resting on the body and being so arranged that a flow of current through the block will magnetize the armature, said armature being adapted to cooperate with the magnetizable body to urge the block against the body whenever the two'are in contact and currentis flowing therebetween.

'magnetized by the flux surrounding the block when a current is passed through the block and being adapted to cooperate with the terminal block to force the latter against the body whenever the two are in contact and current is passing therebetween.

3. A magnetic clamp for establishing a pressure contact between an electrical conductor and a magnetizable body, said clamp including a terminal block adapted to electrically engage the magnetizable body at one end only of said block, a lead secured to the other end of the block, an armature resiliently supported on the block between the ends thereof and so arranged that it will become magnetized by the flux surrounding the block when a current is passed through the block, said armature being held normally out of contact with the magnetizable body and being adapted to urge the terminal block against the body whenever a current is flowing between the terminal block and the body.

4. A magnetic clamp adapted to establish a pressure contact between an electrical conductor and a magnetizable body, said clamp comprising a terminal block, adapted to electrically contact the magnetizable body only at the forward end of the block, the conductor being secured to the other end of the block, an armature associated with the block and supported between the ends thereof, said armature being held normally out of contact with the magnetizable body but being so arranged that a current passing through the block will create a magnetic field around the block which will magnetize the armature, and means associated with the armature and block.for causing the former to urge the latter against the magnetizable body when a current is passing between the block and the body.

5. A magnetic clamp for establishing a pressure contact between an electrical conductor'and a magnetizable body, said clamp including a terminal block, an armature, a spring for supporting the armature on the block and holding the armature normally out of contact with the magnetizable body, said armature being arranged operate with the terminal block to force the latter against the body whenever the two are in contact and current is passing therebetween.

6. A magnetic clamp adapted to establish a pressure contact between an electrical conductor and a magnetizable body comprising a terminal block having contact means on one end for establishing an electrical contact with the mag-Q 

